<template>
    <ul class="list">
        <li class="item" v-for="item of letters" :key="item" :ref="item"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick"
        >{{item}}</li>
        

    </ul>
</template>

<script>
export default {
    name: 'CityAlphabet',
    props: {
        cities: Object
    },
    computed: {
        letters () {
        const letters = []
        for (let i in this.cities){
            letters.push(i)
                                    } 
                   return letters
                   }
    
                    },
    
    data () {
        return {
            touchStatus: false,
            startY: 0,
            timer: null
        }
    },
    updated () {
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods: {
        handleLetterClick (e) {
            this.$emit('change', e.target.innerText)
           
        },
        handleTouchStart () {
            this.touchStatus = true

        },
        handleTouchMove (e) {
            if (this.touchStatus) {
               if (this.timer) {
                   clearTimeout(this.timer)
               }
               this.timer = setTimeout(() => {
                   const touchY = e.touches[0].clientY - 79
                const index = Math.floor((touchY - this.startY) / 20)
               if(index >= 0 && index < this.letters.length){
                   this.$emit('change',this.letters[index])
               }
               },8)
                
               
            }
        },
        handleTouchEnd () {
            this.touchStatus = false
        }
    }
}
</script>
<style lang="stylus" scoped>
    @import '~styles/varibles.styl'
  .list
    display: flex 
    flex-direction: column 
    justify-content: center
    position: absolute
    top: 1.58rem
    right: 0  
    bottom: 0
    width: .4rem
   
    .item
        line-height: .4rem
        text-align: center
        color: $bgColor
</style>